Code of Federal Regulations

Title 14 - Aeronautics and Space
Volume: 1Date: 2024-01-01Original Date: 2024-01-01Title: Section 25.509 - Towing loads.Context: Title 14 - Aeronautics and Space. CHAPTER I - FEDERAL AVIATION ADMINISTRATION, DEPARTMENT OF TRANSPORTATION. SUBCHAPTER C - AIRCRAFT. PART 25 - AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES. Subpart C - Structure. - Ground Loads.
§ 25.509 Towing loads. (a) The towing loads specified in paragraph (d) of this section must be considered separately. These loads must be applied at the towing fittings and must act parallel to the ground. In addition— (1) A vertical load factor equal to 1.0 must be considered acting at the center of gravity; (2) The shock struts and tires must be in their static positions; and (3) With W T as the design ramp weight, the towing load, F TOW, is— (i) 0.3 W T for W T less than 30,000 pounds; (ii) ( 6W T + 450,000)/70 for W T between 30,000 and 100,000 pounds; and (iii) 0.15 W T for W T over 100,000 pounds. (b) For towing points not on the landing gear but near the plane of symmetry of the airplane, the drag and side tow load components specified for the auxiliary gear apply. For towing points located outboard of the main gear, the drag and side tow load components specified for the main gear apply. Where the specified angle of swivel cannot be reached, the maximum obtainable angle must be used. (c) The towing loads specified in paragraph (d) of this section must be reacted as follows: (1) The side component of the towing load at the main gear must be reacted by a side force at the static ground line of the wheel to which the load is applied. (2) The towing loads at the auxiliary gear and the drag components of the towing loads at the main gear must be reacted as follows: (i) A reaction with a maximum value equal to the vertical reaction must be applied at the axle of the wheel to which the load is applied. Enough airplane inertia to achieve equilibrium must be applied. (ii) The loads must be reacted by airplane inertia. (d) The prescribed towing loads are as follows:
Tow pointPositionLoad
MagnitudeNo.Direction
Main gear 0.75 F TOW per main gear unit 1 2 3 4 Forward, parallel to drag axis. Forward, at 30° to drag axis. Aft, parallel to drag axis. Aft, at 30° to drag axis.
Auxiliary gear Swiveled forward 1.0 F TOW 5 6 Forward. Aft.
  Swiveled aft ......do 7 8 Forward. Aft.
  Swiveled 45° from forward 0.5 F TOW 9 10 Forward, in plane of wheel. Aft, in plane of wheel.
  Swiveled 45° from aft ......do 11 12 Forward, in plane of wheel. Aft, in plane of wheel.
[Doc. No. 5066, 29 FR 18291, Dec. 24, 1964, as amended by Amdt. 25-23, 35 FR 5673, Apr. 8, 1970]